RESIDUAL SAR FOCUSING - AN APPLICATION TO COHERENCE IMPROVEMENT

The focusing quality of a SAR processor greatly depends on the accurac y of the system geometry estimate, Sometimes ancillary data do not pro vide enough accuracy, therefore autofocusing has to be performed to ge t the finest quality possible. A ''residual'' azimuth compression is i ntroduced to show how a defocused image can be compensated by means of a monodimensional local operator, The residual transfer function that generates defocusing is then derived, The effects of the defocusing a re shown on both a complex single SAR image and a SAR interferogram, S AR interferograms, however, are much more sensitive to defocusing than the single SAR image, Two algorithms have been developed to estimate, and compensate for, the defocusing in both the single SAR image and S AR interferometric cases, The processors select data suitable for esti mating focusing parameters from the whole images by exploring Kurtosis (for single image focusing) or coherence (for interferometric autofoc using), The residual, short time-domain operator is then exploited to retrieve the focusing parameter values and, finally, to get the focuse d image, The limitations and accuracy of the algorithm in terms of par ameter estimation are investigated, Experimental results, obtained fro m different SAR missions, are presented.